Anatomy of A SPAM Filter (pt 3) : Getting To The Primary Inbox

This is the third installment in our series — if you feel lost, check out our first article and work your way up towards this one.

In our previous articles, we shared key insights from our multi-year study on email deliverability — what SPAM filters are built to look for and how they work.

Using this information, we spent 12 months testing various approaches to sending cold emails (including coming up with new ones).

In this article, we’re going to walk you through the three tactics that proved most effective in getting cold emails to land in the inbox, along with their tradeoffs. We’ll also make recommendations on the ideal audience for each tactic (eg: SDR Teams, Email Agencies, etc).

Let’s go!

Evaluation Framework

When comparing different approaches, we landed on the following criteria to compare and contrast them:

• Cost: how expensive it is to send emails, including setup, maintenance time, software licenses, etc.
• Ramp Time: how long it takes to safely scale sending volume to 1000 emails/domain/day
• Reach: how effective the tactic is at reaching inboxes with different configurations (eg: Google/Office365, Barracuda, Mimecast, Exchange)
• Uptime: ability to consistently deliver, ability to recover in the event that an issue comes up (like blacklisted domain).
• Visibility: how much visibility you have into the health of your sending (eg: getting too many spam reports)
• Sustainability: how future proof the sending technique is, given changes in the industry landscape.

Summary Of Findings

Our findings across the various sending approaches are summarized in this table, with the colors indicating relative performance:

Approach 1: Spam Filter Evasion (domain/inbox rotation)

Spam filter evasion is a bit like guerilla warfare — the idea is that you’re fighting an adversary you can’t take head on (in this case Google/MSFT), so the best chance of success is avoiding facing your adversary at all by getting “lost in the crowd”.

Therefore, this strategy preaches that you create dozens of domains and sending accounts to distribute the email load across them. The theory is that the ESPs need to let at least SOME email through (can you imagine running a business where none of your vendors or partners or prospects can reach you?), so keeping volume low and evenly distributed is the key to success.

Who Is This Best For?

This approach really isn’t the best anymore for anyone except agencies who are selling “management of this complexity” as a value-add service.

The companies that are productizing this approach (Instantly, Smartlead) continue to push the envelope in making it easy for anyone, regardless of their legitimacy as a sender. This means that spammers are piling into this sending method, which has put it squarely in Microsoft/Google’s sights as something to combat. And while they’ve been adapting successfully until recently (eg: now selling pre-aged/pre-warmed domains), there is a physical limit to how much longer they can push the limits of this strategy, as many people have been finding out recently.

Evaluating The Approach

• Cost – MEDIUM: since this model relies on provisioning many Google/Outlook mailboxes, it can get expensive very quickly. Assuming you are sending 30 emails/inbox/day, to send 1000 emails/day would require 33 inboxes, @ $10/month = $300/month. In addition a third party emailing software like Smartlead must also be used at ~$100/month. In addition new domains can cost $15-$50 each to procure and must be renewed yearly.
• Ramp Time – MEDIUM: not only is there a lot of logistical complexity in setting up this complex system, new domains and inboxes need to be aged by at least 1-3 months which makes it difficult to get started right away.
• Reach – MEDIUM: our research has shown clearly that while sending from a reputable ESP gives you more leeway in making mistakes with your sending, it does not give you privileged access to enterprise recipients and you are still just as likely to end up in the spam folder once recipients start marking you as spam.
• Uptime – MEDIUM : our research shows that this sending methodology doesn’t give you any extra privileges for staying out of the spam folder.
• Visibility – LOW: one of the achilles heels of low volume sending is that you can’t get metrics from ESPs on your sending health (spam complaints, etc) unless you hit a minimum volume threshold.
• Sustainability – LOW: the frequency with which ESPs have been clamping down on this methodology keeps going up and its longevity is now severely limited.

Approach 2: Transactional Email Sending

Transactional email sending relies on leveraging an email infrastructure specifically like Mailgun, Sendgrid or Amazon SES to send cold emails.

Who Is This Best For?

This is best for companies who are just starting with cold email, who need to run lots of iterative tests in things like messaging/copy at varying volumes, and who are not necessarily prioritizing reach and deliverability.

Performance

• Cost – LOW: you can get started for $30/month to send thousands of emails.
• Ramp Time – LOW: transactional email accounts can be spun up very fast technically and require the least warmup time.
• Reach – LOW/MEDIUM: enterprises especially block transactional email providers, and bad IP reputation in the pool can land some emails in spam.
• Uptime- HIGH: since people choosing this option aren’t prioritizing deliverability in the first place, you’ll see the same performance without interruptions, unless you’re really getting a lot of spam reports
• Visibility – HIGH: since you can send higher volumes of email, you get the benefit of tools like Google postmaster tools, as well as reports from FBLs if you’re emailing non b2b emails.
• Sustainability – LOW: sending cold email through these services is a direct violation of their Terms of Service and they can shut you down at any time, permanently, so this should be considered a service in the early days.

Approach 3: Be A Legitimate Sender

This is the opposite of the last two approaches, and involves you building a custom solution whereby you take control of your domain and IP authority, and build up a dedicated email sending program.

This can work either by getting a dedicated email server by building it yourself, using a SaaS product (Kitt AI, Mailreef, Infraforge, etc) or using a managed services provider (Senders.co).

Who Is This Best For?

This is best for marketing / sales teams who are running a proper Go-To-Market strategy, who are past the phase of “throwing stuff at the wall”, “spraying and praying, etc” and who care about inbox placement/reach.

First, you’re likely to be sending higher quality email traffic at a reasonable level, which is the requirement for building reputation as a legitimate sender. Second, the ‘evasion’ strategy is too expensive to logistically and physically run across large groups of senders. Finally, you need a sustainable solution whereby you aren’t waking up to Google/MSFT doing an algorithm change and wrecking your program at once (as they’ve done multiple times since 2020 to Gmail/Outlook senders)

Performance

• Cost – MEDIUM: although there are more and more services popping up selling dedicated email servers, the cost of this is going down fast, although the ones guaranteeing inbox placement (like Kitt AI’s Delivery Machine) will still charge a premium.
• Reach – HIGH: many people don’t know that many enterprises block regular Gmail/Outlook b2b accounts, in addition to transactional email traffic. Private email servers have the best deliverability.
• Ramp Time – MEDIUM: the technical side of this approach is very fast, since you’re working with limited domains/mailboxes and the server provider manages all of your DNS records. However, there needs to be a gradual increase in traffic for the first 30-90 days, which is more than the transactional email route
• Uptime – HIGH : Dedicated IPs ensures nobody else’s traffic can unexpectedly impact yours. Having multiple IP addresses and support for secondary domains gives you backup options. Jailbreak technology (offered by Kitt AI) enables you to get out of the spam folder quickly if you do somehow end up getting caught in there.
• Visibility – HIGH: sending from fewer domains means it’s easier to hit the thresholds required by Google Postmaster tools.
• Sustainability – HIGH: ESPs will always have to leave the door open to legitimate senders. They may raise the bar, but a door that’s always shut isn’t a door at all, and commerce requires legitimate email communications to remain open.

Conclusion

Most email senders have felt the major changes in email deliverability over the past two years, and they can see that email as a channel is unlikely to survive if it continues on its current path. Our 2 year email research confirmed this suspicion, but also helped us find alternate approaches to sending that the “influencers” told us were simply not possible (eg: operating your own email sending infrastructure).

We will continue to publish the latest and greatest findings from the Deliverability Lab to give you every edge in getting to the inbox — subscribe to our blog below to stay in the loop.